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Our long-term memory system is thought to have an unlimited capacity. Once information goes in, it stays there forever. So, the failure to remember something is not because the information has dropped out of our system. Rather, memory problems often stem from problems with people's ability to retrieve some of the knowledge that they possess. Long-term memory can be retrieved by giving information good 'tags' (e.g. strong verbal and imagery codes), when it is initially encoded, or by searching the tags properly to find it.
Another feature of our long-term memory system is that our emotional state ay the time of learning and at the time of recall affects retention. When the mood a person is in during learning matches the mood he is in when asked to recall, retention is improved. When a sad mood is evoked, people remember more unpleasant past experiences than when a happy mood is engendered. Similarly, people remember more happy childhood experiences when asked to get themselves into a happy mood. This kind of research gives us a clue that part of the memory tag or metadata for the things we learn contains information about our emotional state at the time of learning.
So, we can see that emotional cues may help to facilitate retrieval of memories up to a point. Happy mood - more likely to have happy memories - and if we are grumpy, we are more likely to retrieve negative memories. But extremely strong emotions can interfere with trying to recall information rather than facilitating retrieval. For example, sitting an exam for a test-anxious student isn't going to help with performance.
The retrieval of memories is a dynamic process - it is more than just flicking through a register of memories and calling it up into consciousness. Recall forces us to reconstruct, reproduce or recreate the original information we encoded from a variety of memory metadata, including our memory at the time we learned the information, and the emotion at the time we are trying to call it. To this extent, what we remember changes.
Next week, I'll talk about some simple techniques for improving your memory.